// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_
#define NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_

#include <map>
#include <set>
#include <string>

#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/threading/non_thread_safe.h"
#include "base/threading/platform_thread.h"
#include "net/base/net_export.h"
#include "net/base/network_change_notifier.h"
#include "net/url_request/url_request_throttler_entry.h"
#include "url/gurl.h"

namespace net {

class BoundNetLog;
class NetLog;

// Class that registers URL request throttler entries for URLs being accessed
// in order to supervise traffic. URL requests for HTTP contents should
// register their URLs in this manager on each request.
//
// URLRequestThrottlerManager maintains a map of URL IDs to URL request
// throttler entries. It creates URL request throttler entries when new URLs
// are registered, and does garbage collection from time to time in order to
// clean out outdated entries. URL ID consists of lowercased scheme, host, port
// and path. All URLs converted to the same ID will share the same entry.
class NET_EXPORT URLRequestThrottlerManager
    : NON_EXPORTED_BASE(public base::NonThreadSafe),
      public NetworkChangeNotifier::IPAddressObserver,
      public NetworkChangeNotifier::ConnectionTypeObserver {
public:
    URLRequestThrottlerManager();
    ~URLRequestThrottlerManager() override;

    // Must be called for every request, returns the URL request throttler entry
    // associated with the URL. The caller must inform this entry of some events.
    // Please refer to url_request_throttler_entry_interface.h for further
    // informations.
    scoped_refptr<URLRequestThrottlerEntryInterface> RegisterRequestUrl(
        const GURL& url);

    // Registers a new entry in this service and overrides the existing entry (if
    // any) for the URL. The service will hold a reference to the entry.
    // It is only used by unit tests.
    void OverrideEntryForTests(const GURL& url, URLRequestThrottlerEntry* entry);

    // Explicitly erases an entry.
    // This is useful to remove those entries which have got infinite lifetime and
    // thus won't be garbage collected.
    // It is only used by unit tests.
    void EraseEntryForTests(const GURL& url);

    // Turns threading model verification on or off.  Any code that correctly
    // uses the network stack should preferably call this function to enable
    // verification of correct adherence to the network stack threading model.
    void set_enable_thread_checks(bool enable);
    bool enable_thread_checks() const;

    // Whether throttling is enabled or not.
    void set_enforce_throttling(bool enforce);
    bool enforce_throttling();

    // Sets the NetLog instance to use.
    void set_net_log(NetLog* net_log);
    NetLog* net_log() const;

    // IPAddressObserver interface.
    void OnIPAddressChanged() override;

    // ConnectionTypeObserver interface.
    void OnConnectionTypeChanged(
        NetworkChangeNotifier::ConnectionType type) override;

    // Method that allows us to transform a URL into an ID that can be used in our
    // map. Resulting IDs will be lowercase and consist of the scheme, host, port
    // and path (without query string, fragment, etc.).
    // If the URL is invalid, the invalid spec will be returned, without any
    // transformation.
    std::string GetIdFromUrl(const GURL& url) const;

    // Method that ensures the map gets cleaned from time to time. The period at
    // which garbage collecting happens is adjustable with the
    // kRequestBetweenCollecting constant.
    void GarbageCollectEntriesIfNecessary();

    // Method that does the actual work of garbage collecting.
    void GarbageCollectEntries();

    // When we switch from online to offline or change IP addresses, we
    // clear all back-off history. This is a precaution in case the change in
    // online state now lets us communicate without error with servers that
    // we were previously getting 500 or 503 responses from (perhaps the
    // responses are from a badly-written proxy that should have returned a
    // 502 or 504 because it's upstream connection was down or it had no route
    // to the server).
    void OnNetworkChange();

    // Used by tests.
    int GetNumberOfEntriesForTests() const { return url_entries_.size(); }

private:
    // From each URL we generate an ID composed of the scheme, host, port and path
    // that allows us to uniquely map an entry to it.
    typedef std::map<std::string, scoped_refptr<URLRequestThrottlerEntry>>
        UrlEntryMap;

    // Maximum number of entries that we are willing to collect in our map.
    static const unsigned int kMaximumNumberOfEntries;
    // Number of requests that will be made between garbage collection.
    static const unsigned int kRequestsBetweenCollecting;

    // Map that contains a list of URL ID and their matching
    // URLRequestThrottlerEntry.
    UrlEntryMap url_entries_;

    // This keeps track of how many requests have been made. Used with
    // GarbageCollectEntries.
    unsigned int requests_since_last_gc_;

    // Valid after construction.
    GURL::Replacements url_id_replacements_;

    // Certain tests do not obey the net component's threading policy, so we
    // keep track of whether we're being used by tests, and turn off certain
    // checks.
    //
    // TODO(joi): See if we can fix the offending unit tests and remove this
    // workaround.
    bool enable_thread_checks_;

    // Initially false, switches to true once we have logged because of back-off
    // being disabled for localhost.
    bool logged_for_localhost_disabled_;

    // NetLog to use, if configured.
    BoundNetLog net_log_;

    // Valid once we've registered for network notifications.
    base::PlatformThreadId registered_from_thread_;

    DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerManager);
};

} // namespace net

#endif // NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_
